# Digit Sum Calculator

URL: https://speedycalculator.com/calculators/math/sum-of-digits/
Last updated: 2026-10-30

> The digit sum calculator adds the digits of one or more numbers, gives the digital root or alternating digit sum, and shows how often each digit occurs.

## Inputs

- Numbers (separate with commas)
- I want to find
- Treatment of numbers

## Results

- Result
- Digit table

## Formula

```
Digit sum = Σ digits;  digital root = repeated digit sum;  alternating sum = d₀ − d₁ + d₂ − …
```

## Explanation

Digit sums underlie divisibility tests (3, 9 and 11), checksums and number puzzles. Seeing the count of each digit also helps when checking long numbers such as IDs or serial numbers.

### How to use the Digit Sum Calculator

- **Numbers (separate with commas)**
- **I want to find**
- **Treatment of numbers**

Everything is calculated in your browser, so results appear instantly and nothing you type is sent to a server.

### How it works

Choose what to find and whether to treat all numbers as one group or separately. The table lists each digit, how often it appears and its contribution to the total.

## Worked example

Inputs — Numbers (separate with commas): 1234, 5678; I want to find: Sum of digits; Treatment of numbers: As a single group.

Results — **Result = 36**; Digit table = Digit Count Sum
1 1 1
2 1 2
3 1 3
4 1 4
5 1 5
6 1 6
7 1 7
8 1 8
Total 8 36.

## Key terms

- **Digit sum**: The sum of the digits of a number.

## FAQ

**What is the digit sum of 1234?**
1 + 2 + 3 + 4 = 10.

**How does the digit sum test divisibility?**
A number is divisible by 3 (or 9) when its digit sum is.

**What is the alternating digit sum for?**
Divisibility by 11.

**What is the digital root of 1234?**
1 (10 → 1).


## Sources

- [OpenStax – Prealgebra 2e](https://openstax.org/details/books/prealgebra-2e)
- [Wolfram MathWorld – Digit sum](https://mathworld.wolfram.com/DigitSum.html)